High Testosterone and High Prolactin

I wrote about this recently. Wikipedia is really getting bad for validity of information. The study cited for that claim is from 1985... Many studies since then have elucidated the actual mechanism.

http://62.182.86.140/scimag/7026711/Neurotoxicity%20of%20pyridoxine%20analogs%20is%20related%20to%20coenzyme%20structure%20%28Molecular%20and%20Chemical%20Neuropathology%20%28Neurochemical%20Pathology%29%2C%20vol.%203%2C%20issue%203%29%20%281985%29.pdf

The observation that the phosphorylated derivative was not toxic also suggested that it was not a physical effect of the molecule on the cell membrane that produced cell injury. Several mechanisms might account for the correlation between ability to serve as active coenzyme and toxic effect. In high concentrations, pyridoxine compounds combine together or with a second unidentified intracellular constituent to inhibit the pyridoxal. This might involve the formation of a hydrazone or other molecule similar to that produced with isoniazid (McCormick and Snell, 1959; McCormick et al., 1960; McCormick and Snell, 1961). These derivatives inhibit pyridoxal kinase (ATP:pyridoxal 5-phosphotransferase, EC 2.7.1.35) that catalyzes the production of the phosphorylated coenzymes from pyridoxine, pyridoxal, or pyridoxamine. The nonphosphorylated compounds are inactive as coenzymes and presumably binding to pyridoxal phosphate-dependent enzymes is low. However, if the concentration is high enough, nonphosphorylated derivatives may bind competitively at the coenzyme site and block active coenzyme binding (Rudman and Williams, 1983). There is evidence that coenzyme attachment to the apoenzyme involves binding at two different sites on the molecule (Shive and Lansford, 1980). In massive doses, two coen- zyme molecules might become bound to the active site, one at each of the usual binding sites, rendering the enzyme inactive. At least one enzyme, pyridoxal kinase, is inhibited by excessive amounts of pyridoxal. However, in the latter case pyridoxal is the substrate rather than the coenzyme. The favored hypothesis is that one specific enzyme system is inhibited by excess pyridoxine or its analogs. If this were pyridoxal kinase one might expect inhibition of many pyridoxal phosphate-dependent enzyme systems. However, the animals and the humans who were studied extensively (Schaumburg et al., 1983; Windebank et al., in press) did not show any systemic ill effects. This suggests that either there is an enzyme system (that might be a neuron-specific pyridoxal kinase) restricted to neurons in general or to DRG neurons in particular. The former possibility might be manifested only at the DRG level because increasing blood levels of pyridoxine did not increase the levels in the central nervous system (Spector, 1978a,b; Bender and Totoe, 1984), because of the presence of an apparent BBB and a saturable uptake mechanism for these compounds (Spector, 1978a,b). However, as discussed above, the BBB is less competent at the DRG and toxin concentrations are potentially much higher than at other places in the peripheral or central nervous system.

In this 1985 paper they showed it was only an issue with nonphosphorylated B6 derivatives. They even postulated what was later proved to be true, that it was a competitive inhibition of enzyme inhibition by nonphosphorylated compounds. This does NOT apply to the phosphorylated P5P form. Later studies proved the mechanism.

https://pubmed.ncbi.nlm.nih.gov/28716455/

In the present study, the neurotoxicity of the different forms of vitamin B6 is tested on SHSY5Y and CaCo-2 cells. Cells were exposed to pyridoxine, pyridoxamine, pyridoxal, pyridoxal-5-phosphate or pyridoxamine-5-phosphate for 24h, after which cell viability was measured using the MTT assay. The expression of Bax and caspase-8 was tested after the 24h exposure. The effect of the vitamers on two pyridoxal-5-phosphate dependent enzymes was also tested. Pyridoxine induced cell death in a concentration-dependent way in SHSY5Y cells. The other vitamers did not affect cell viability. Pyridoxine significantly increased the expression of Bax and caspase-8. Moreover, both pyridoxal-5-phosphate dependent enzymes were inhibited by pyridoxine. In conclusion, the present study indicates that the neuropathy observed after taking a relatively high dose of vitamin B6 supplements is due to pyridoxine. The inactive form pyridoxine competitively inhibits the active pyridoxal-5'-phosphate. Consequently, symptoms of vitamin B6 supplementation are similar to those of vitamin B6 deficiency.

High levels of pyridoxine can inhibit the P5P enzymes, causing a drop in B6 function. So taking too much pyridoxine fucks up the body's ability to create the active P5P form. Supplementing P5P itself does NOT have that effect. There have been no documented cases of B6 toxicity from P5P. If your read the papers, it's actually a REDUCTION in P5P from too much pyridoxine inhibiting the enzyme used to convert B6 to its active P5P form. This is why toxicity from too much pyridoxine acts more like a P5P deficiency, because that's what it really does. It lowers the active P5P form by competitively binding and inhibiting the enzyme responsible for making P5P.

https://www.sciencedirect.com/science/article/pii/S221343442030013X?via%3Dihub

Whereas the dose of vitamin B6 in the supplements was previously considered responsible for causing neuropathy [[8], [9], [10]], our previous data indicated that the vitamer present in the supplement is the more important determinant [7]. Of all B6 vitamers, only PN was shown to have cytotoxic effects on cultured neuronal cells. These findings correlate well with in vivo animal studies, where PN induced neuronal damage after intraperitoneal injection, whereas the other vitamers did not induce any damage [11]. Also clinically, the vitamer PN predominantly seems to be causing adverse health effects, as the majority of reported cases to Lareb concerned supplements that contain the inactive vitamer PN. It must be noted that most of the vitamin B6 preparations on the market also contain PN, which could contribute to an overrepresentation of PN induced cases of neuropathy. However, this still highlights that, besides the dose of vitamin B6, the specific vitamer present in the supplements plays an important role in the development of vitamin B6-related neuropathy. Some of the patients reporting neuropathic complaints only used a daily dose of 2 mg vitamin B6, whereas other cases of neuropathy developed after the use of 250 mg. In addition, large differences in plasma levels of PLP between the different cases of B6-induced neuropathies were reported by Lareb [5]. This implies that there seems to be an inter-individual difference in kinetics of vitamin B6 and sensitivity towards its toxicity. Taking into account our in vitro findings, we hypothesized that the accumulation of free PN would be responsible for the toxic effects.

They state there that pyridoxine is the only one that causes toxicity. Then look at the other conclusions in the study.

As expected, supplementation with PLP did barely increase plasma PN levels, since PLP is pharmacologically active and does not need to be transformed into PN. PN was detectable in plasma (5.9 nmol/L) in only one participant. The detected concentration is comparable with low plasma concentrations of PN in the placebo group reported by Bor et al. [20]. The presence of PN intracellularly or in CSF after PLP supplementation can be explained by the presence of proteins with pyridoxal reductase activity, which was recently revealed in vitro and in vivo by Ramos et al. [19].

So P5P, or PLP as they label it in this study, does NOT increase pyridoxine levels. It was only detectable in one patient at all.

Taking into account our in vitro findings, we hypothesized that the accumulation of free PN would be responsible for the toxic effects.

Free pyridoxine is the issue, and that only happens by taking large amounts of pyridoxine.

Differences in metabolism of PN after supplementation possibly explains the individual differences in sensitivity to the neuropathic effects of vitamin B6. Hence, not only the dose, but also the vitamer present in the vitamin B6 supplements is important for the development of such adverse health effects. This is also presented by the data from Lareb, showing that more than 96 % of the reports is due to the use of PN in the supplements. The fact that the vast majority of the available vitamin B6 supplements contain PN must be taken into consideration here.

Pyridoxine is the issue, not P5P. Moreover, it's only an issue in people with the mutation that prevents them from converting pyridoxine to P5P efficiently. So some people can take high levels of pyridoxine without issue. They study even suggests people taking P5P instead.

Ultimately, instead of lowering the dose, it might be better to replace PN by PLP or PL in the supplements.

P5P is safe, and does not have the issue that pyridoxine has. Wikipedia needs to be updated, because I have seen multiple people citing this online now. It's spreading misinformation.